When a drug is systemically administered through an oral route and by an intravenous injection, the drug is supplied to not only a focal site as a dosing target but also to normal tissue. As a result, adverse side effects due to the drug administration are observed, and in some cases, the therapeutic method must be changed or discontinued. In order to reduce adverse side effects, a drug referred to as a molecular target drug having a specific binding ability to a molecular marker such as a receptor, a ligand, and an enzyme peculiar to a dosing target has been developed (see H Asahina, et al., “A phase II trial of gefitinib as first-line therapy for advanced non-small cell lung cancer with epidermal growth factor receptor mutations”, British Journal of Cancer (2006) 95, pp. 998-1004). However, at present, such a molecular target drug has not been able to sufficiently reduce adverse side effects such as the occurrence of interstitial pneumonitis caused by the administration of gefitinib, and further, does not exhibit a sufficient therapeutic effect at the focal site.
In order to specifically supply a drug to a dosing target and maintain an optimum drug concentration in the vicinity of the dosing target, a technology referred to as a drug delivery system (DDS) is attracting attention. WO 2002/087497 discloses an active targeting polymer conjugate DDS in which a drug and a ligand are bound to a synthetic polymer.